PhD thesis of Thibault Androuin (Université Bretagne - Loire) defended on 13/12/2018
The slipper limpet (Crepidula fornicata) is an invasive species of European coasts. Protandric hermaphrodite, this gregarious species forms individuals' stacks which accumulate in high density on bottom. For a long time considered as a detrimental invader, the slipper limpet is also an ecosystem engineer, modifying its habitat both physically and biologically. It is model to study how invasive and engineer species can structure and modify the ecosystem that they colonize.
In this Ph.D. thesis, these effects have been examined through the trophic functioning of habitats colonized by the slipper limpet, with a special reference to the primary benthic production. Experimental stimulation of subtidal microphytobenthos (MPB) has been demonstrated by the biological activity of the slipper limpet.The trophic niche of C. fornicata has been redefined following the discovery of the presence of carbonate spherules in its tissues, overestimating the contribution of MPB in its diet. Several trophic markers use (pigments, fatty acids, isotopes) revealed that young motile individuals were likely to graze the MPB associated to shell biofilm. Sessile adults, were likely opportunistic filter-feeders, where detritus but also MPB contribute to their trophic diet.
The analysis of several filter-feeders inhabiting Crepidula beds has demonstrated that the slipper limpet was not a trophic competitor for commercially important species (black scallop and flat oyster) due to their trophic sorting mechanisms. At the food web scale, the high density of slipper limpet can lead to a homogenization of the global food web due to organic matter enrichment. Dead Crepidula bed showed trophic complexity similar to maerl bed, which is a high biodiverse ecosystem. This thesis, in addition to characterize the trophic functioning of Crepidula beds, shows that an invasive species, in facilitating different biological compartments (MPB, filter-feeders), can contribute to the ecosystem richness such as the Bay of Brest.